Field of the Invention
The present invention generally relates to a focus detecting device for multi-point focus detection in which a combination of an axial focus detection area and an off-axial focus detection area is employed.
In the multi-point focus detection in which not only is the axial focus detection area employed, but the off-axial focus detection area is also employed, the use of an optical system for axial focus detection as an optical system for off-axial focus detection will bring about the following problems. Specifically, if the off-axial focus detection area is spaced a distance from the optical axis in order to avoid any possible interference between an axial light flux for the axial focus detection and an off-axial light flux for the off-axial focus detection, the off-axial focus detection optical system for receiving a light flux from the off-axial focus detection area of the object must also be spaced a sufficient distance from the optical axis. Accordingly, a CCD (charge-coupled device) chip in which a plurality of CCDs, each of which has a plurality of light receiving elements, are formed on a single chip tends to become bulky in size, rendering an AF (auto-focus) module to be correspondingly bulky in size and high in manufacturing cost. On the other hand, if the size of the CCD chip is reduced, the off-axial light flux will become so close to the on-axis light flux as to result in the undesirable interference between these light fluxes, rendering an optical system such as condenser lenses, etc., to be very complicated.